1. Field of the Invention
This invention relates to a thermal printhead for use in a recording machine, such as a printer and a facsimile machine, for thermally recording characters in the form of a dot matrix on heat-sensitive paper in accordance with an electrical image signal supplied thereto, and particularly to a so-called edge type thermal printhead with a plurality of driving circuits arranged in a single array along one side of a linear thermal array comprised of a plurality of heat-producing elements.
2. Description of the Prior Art
Direct-drive type thermal printheads having directly mounted I.C. drivers, such as MSI and LSI intergrated circuit drivers, are well known in the art. Such thermal printheads may be generally divided into two categories. In one category, called the center type, I.C. drivers are provided on both sides of a linear thermal array of heat-producing elements; whereas, in the other category, called the edge type, I.C. drivers are provided only along one side of the linear thermal array. There are advantages and disadvantages in either of these categories.
The largest disadvantage of the edge type thermal printhead has been said to be difficulty in increasing the array density of heat-producing elements, each of which constitutes a picture element or pixel to form a so-called "burn point" on heat-sensitive paper when activated by passing a driving current therethrough. For example, in providing I.C. driver chips directly on a thermal printhead for controlling heat-producing elements 32 per chip by the tape carrier method, it has been difficult to arrange the I.C. chips at a pitch of 8 mm or less. Thus, even in the case where the array pitch of 8 dots/mm may be attained with all of the remaining specifications satisfied if use is made of the center type structure, the only array density of 4 dots/mm may be attained if I.C. driver chips are provided in the edge type structure. As a result, utilization of the edge type structure effectively inhibits the application of the thermal printhead to recording machines requiring high density recording, such as facsimile machines.
On the other hand, an edge type thermal printhead may be manufactured relatively easily as compared with that of the center type. Another important advantage of the edge type thermal printhead is that recorded images can be inspected immediately since they appear as soon as they are recorded. Thus, there has been a long felt need to increase the recording density and thus the heat-producing array density of an edge type thermal printhead.